This invention relates to a hydrogenated block copolymer or hydrogenated block copolymer mixture obtained by hydrogenating a star-branched structure-containing block copolymer or block copolymer mixture, respectively, said hydrogenated block copolymer or hydrogenated block copolymer mixture being excellent in various properties such as heat resistance, weather resistance, flow properties and the like and also excellent in the improving effect on impact resistance, heat resistance, stiffness, processibility, appearance of molded article and the like as a modifier for other thermoplastic resins; and can give, when blended with other rubbery polymers, a thermoplastic elastomer composition excellent in mechanical properties. This invention also relates to a hydrogenated block copolymer composition obtained by blending the above-mentioned hydrogenated block copolymer or hydrogenated block copolymer mixture with a thermoplastic resin and/or a rubbery polymer, said composition being a thermoplastic resin composition excellent in balance of impact resistance, heat resistance, processibility, appearance of molded article and the like or a thermoplastic elastomer composition excellent in mechanical properties.
Diene copolymers having double bonds in the polymer chain are inferior in thermal stability, weather resistance and ozone resistance. Therefore, in order to overcome these disadvantages, it has been known to hydrogenate the double bonds. Methods for the hydrogenation are proposed in, for example, Japanese Patent Application Kokoku No. 45-39,275 and No. 45-3,555; Japanese Patent Application Kokai No. 56-62,805 and No. 59-133,203 and the like. The hydrogenated polymers obtained by these methods exhibit heat resistance, weather resistance and ozone resistance as expected, so that they are often used in the quality-improvement of resins. Also, as a polymer excellent in thermal stability and weather resistance, ethylene-.alpha.-olefin copolymers and the like are known. However, these polymers are not satisfactory to obtain a composition having a good balance of impact resistance, heat resistance, stiffness, processibility and appearance of molded article by blending them with a thermoplastic resin.